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51.
Several techniques and a software tool for reliability analyses that generally apply to fault-tolerant systems operating in phased-missions are given. Efficient models, using Markov chains without an explosion of the state space, are provided for missions consisting of multiple phases, during which the system configuration or success criteria can change. In different phases, the failure rates and the fault and error handling models can also change, and the duration of any phase can use deterministic or random models. An efficient reconfiguration procedure that is computationally more efficient than any existing technique is developed. The technique is demonstrated using a numerical example to show the effects of mission phases on the system reliability 相似文献
52.
For the last five years, the Structures, Materials and Propulsion Laboratory of the Institute for Aerospace Research, National Research Council of Canada, has devoted a significant amount of effort investigating powder metallurgy gamma titanium aluminides. The main results of the studies on microstructural evolution, hot workability, creep behaviour and microstructure-mechanical property relationships for P/M gamma alloys are reviewed in this article. Work is in progress to apply the knowledge gained to cast gamma alloys for gas turbine applications. 相似文献
53.
NO Reduction with Hydrogen over Cobalt Molybdenum Nitride and Molybdenum Nitride: A Comparison Study
Cobalt molybdenum nitride (Co3Mo3N) and molybdenum nitride (Mo2N) were investigated for the catalytic reduction of NO with H2. The latter deactivated rapidly with time on stream, whereas the former remained active and stable over a test period of 30 h. The results of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and H2-temprature-programmed reduction (H2-TPR) characterization indicated that the deactivation of Mo2N was due to the bulk oxidation of Mo2N to MoO2. As for the Co3Mo3N catalyst, despite partial decomposition into Mo2N and Co, it remained resistant to oxidation. The results suggest that compared to the monometallic nitride, the bimetallic one is more suitable for NO reduction with H2. 相似文献
54.
In high-speed networks, a congestion control strategy has to manage bandwidth allocation based on the characteristics of input traffic sources. Accordingly, the definition of traffic characterization becomes significant in all aspects concerning network performance. In this paper, the burstiness characterization of a traffic stream is based on a virtual queue principle. We study the leaky bucket mechanism as a regulator element that controls input traffic before access to a newwork, as well as inside a network. To protect an input traffic stream, we investigate the optimal parameter settings of a leaky bucket. In addition, we analyse the worst case performance, and obtain upper bounds on loss probability and packet delay. We also determine the characteristics of an output stream in the worst case. Such performance bounds reveal the effectiveness of a leaky bucket, and provide enough information for the QOS satisfaction of the network users. 相似文献
55.
Er-Jun Li Kai Xia Shuang-Feng Yin Wei-Li Dai Sheng-Lian Luo Chak-Tong Au 《Materials Chemistry and Physics》2011,125(1-2):236-241
A series of Bi2O3–MgO composites were synthesized by solvent-thermal method. It was found that the Bi2O3–MgO composites perform much better than TiO2 (P25), Bi2O3 and MgO in the photocatalytic degradation of rhodamine B (RhB) in the presence of HCl and under irradiation of visible light (λ > 400 nm). The effects of Bi/Mg molar ratio, crystallization temperature of Bi2O3–MgO and reaction conditions on photocatalytic activity were studied. The best performance was observed over the composite with Bi:Mg molar ratio equal to 2:1 that had been subject to crystallization at 120 °C for 20 h. In addition, the photocatalytic efficiency of the composite can be significantly enhanced by the presence of hydrochloric acid. The prepared samples were characterized by XRD and UV–vis DRS techniques. The relationships between the structure and photocatalytic performance of the as-prepared Bi2O3–MgO samples were also investigated. 相似文献
56.
Magnetic, ferroelectric and magnetoelectric coupling properties of Fe-implanted BaTiO3 films 总被引:1,自引:0,他引:1
BaTiO3 (BTO) nano-films were implanted with iron by means of ion-implantation. According to the results of X-ray diffraction (XRD) and Raman analysis, all the films are single-phase with tetragonal structure. Upon the increase of Fe dosage, on one hand, there is a decrease in c/a ratio of the unit cells. As the grain size and surface roughness of the Fe-implanted films decrease, the well crystallized film was obtained. Consequently, both decreasing of coercivity and boosting of magnetization were observed simultaneously. With the decline of the grain size and surface roughness during thermal treatment of the Fe-implanted films, there is an improvement of Fe distribution across the BTO matrix. Consequently, there is a decrease of coercivity and rise of magnetization. Upon the decrease of Fe dosage, on the other, there is a decline in magnetization, and a ferroelectric hysteresis loop is observed at a Fe dosage of 3.0 × 1014 cm− 2. Additionally, the dependence of capacitance on the applied magnetic field and its frequency were also monitored. 相似文献
57.
Hanliang Zhu K. Maruyama D. Y. Seo P. Au 《Metallurgical and Materials Transactions A》2005,36(5):1339-1351
XD TiAl alloys (Ti-45 and 47Al-2Nb-2Mn+0.8 vol pct TiB2) (at. pct) were oil quenched to produce fine-grained fully lamellar (FGFL) structures, and aging treatments at different
temperatures for different durations were carried out to stabilize the FGFL structures. Microstructural examinations show
that the aging treatments cause phase transformation of α
2 to γ, resulting in stabilization of the lamellar structure, as indicated by a significant decrease in α
2 volume fraction. However, several degradation processes are also introduced. After aging, within lamellar colonies, the α
2 lamellae become finer due to dissolution, whereas most of the γ lamellae coarsen. The dissolution of α
2 involves longitudinal dissolution and lateral dissolution. In addition, at lamellar colony boundaries, lamellar termination
migration, nucleation and growth of γ grains, and discontinuous coarsening occur. With the exception of longitudinal dissolution, all the other transformation
modes are considered as degradation processes as they result in a reduction in α
2/γ interfaces. Different phase transformation modes are present to varying degrees in the aged FGFL structures, depending on
aging conditions and Al content. A multiple step aging reduces the drive force for phase transformation at high temperature
by promoting phase transformation via longitudinal dissolution at low temperatures. As a result, this aging procedure effectively
stabilizes the lamellar structure and suppresses other degradation processes. Therefore, the multiple step aging is suggested
to be an optimal aging condition for stabilizing FGFL XD TiAl alloys. 相似文献
58.
In this paper, a novel semi-empirical modeling method to mathematically derive a nonlinear equivalent circuit from a special group of impedance fuel cell models is proposed. As an example, a 5-cm2 direct methanol fuel cell (DMFC) was modeled by this method. The derived equivalent circuit is composed of lumped nonlinear resistors, capacitors and an inductor. The nonlinear circuit has an impedance equivalent to the target fuel cell in various operating conditions and provides a good approximation of the static and transient behaviors of the fuel cell. The equivalent circuit fuel cell model was validated by comparing its numerical simulation results with its polarization curve and the dynamic behavior of the target DMFC. These comparisons were performed while the DMFC was operating under square current pulses with different upper and low current levels. 相似文献
59.
本文对双向联想记忆(BAM)的学习与回忆过程进行了详细的分析。在学习过程中,先是运用自适应非对称BAM算法进行学习,进而采用设置印象门限的反复记忆算法进行学习,本文从理论上证明了印象门限与样本吸引域之间的关系,指出反复记忆方法的理论依据。回忆过程中,采用非零阈值函数的运行方程,提出了阈值学习方法,并且从理论上证明了非零阈值函数的运行方程的采用,可进一步扩大吸引域。为了进一步扩大网络的信息存储量,本文引入了并联的BAM结构。本文方法的采纳,使得BAM网络的信息存储量、误差校正能力等得到很大程度的提高。 相似文献
60.
A patient with angina pectoris who had been successfully treated by thoracoscopic cardiac sympathectomy was scheduled to have scalp debridement under general anaesthesia for a scald burn. There were haemodynamic changes during and after the operation including anaesthetic induction, endotracheal intubation, maintenance, and early recovery period. The sympathetic denervated heart showed little chronotropic response to anaesthetic and surgical stimulation. On the contrary, the parasympathetic response was predominant. An episode of severe bradycardia occurred during endotracheal suctioning prior to extubation. The haemodynamic response to cardiac sympathetic denervation corresponded to the efferent effect of beta-receptor blockade 相似文献